(1) In a criminal case, the following evidence is admissible, if otherwise admissible under these rules:

(A) evidence of specific instances of sexual behavior by the alleged victim offered to prove that a person other than the accused was the source of semen, injury, or other physical evidence;

As this latter Rule makes clear, such evidence of other sexual behavior is not automatically admissible; instead, it must be "otherwise admissible under the rules of evidence. This qualifying language was the problem for tha appellant in United States v. Seed, 2009 WL 2045690 (8th Cir. 2009).

In Seed, a jury found Jason Adam Pumpkin Seed guilty of the sole count of an indictment charging him with aggravated sexual abuse and attempted aggravated sexual abuse. This sexual abuse was allegedly committed against Heather Red Cloud, and at trial, the prosecution proved its case in part through presenting evidence of Red Cloud's extragenital injuries resulting from the alleged abuse.

In turn, Pumpkin Seed sought to introduce evidence that those injuries could have been caused by two sexual encounters that Red Cloud with different men within days of the alleged rape. The district court excluded this evidence, prompting Pumpkin Seed's appeal. In that appeal, the Eight Circuit noted that Pumpkin Seed's evidence was arguably admissible under Federal Rule of Evidence 412(b)(1)(A), but only if the evidence was "otherwise admissible" under the rules of evidence.

The Eighth Circuit found, however, that it was not otherwise admissible because

First, Pumpkin Seed did not make any offer of proof concerning the circumstances of Red Cloud's past sexual activity from which the district court could assess the likelihood of her injuries being caused by her consensual sexual activity....Absent such an offer of proof, we cannot say that the district court abused its discretion in determining that the type and extent of physical injuries present on Red Cloud are generally inconsistent with consensual sexual intercourse, thereby suggesting that the disputed evidence concerning Red Cloud's consensual relationships has little or no probative value in providing an alternate source for her injuries....Second, the probative value of this evidence is substantially outweighed by the high risk of unfair prejudice and confusion of the issues posed by admitting evidence that Red Cloud was involved in at least two sexual encounters with different men, one of whom was married, within days of the alleged rape.

The court thus found that the evidence failed the Rule 403 balancing test and affirmed the district court's opinion.